Field of the Invention
The present disclosure relates to a technique for fabricating a transition metal chalcogenide (TMC), and more particularly, to a method of fabricating a transition metal chalcogenide in large scale and an apparatus used for the method.
Description of the Related Art
A conventional technique for fabricating a chalcogenide thin-film is known (e.g., Korean Patent Open Publication No. 10-2007-80940, published on May 25, 2015).
Transition metal dichalcogenides (TMDs) are materials having planar structures having a single layer constituted of 3 atomic layers, similar to that of graphene having a single carbon atomic layer. Unlike graphene having metalloid characteristics, transition metal dichalcogenides exhibit characteristics of an n-type semiconductor, a p-type semiconductor, or a bipolar semiconductor according to the constituent materials of the transition metal dichalcogenides. Furthermore, since the transition metal dichalcogenides have thicknesses smaller than or equal to several nanometers, the transition metal dichalcogenides are highly useful for flexible devices and transparent devices so that it may be a promising material fields of nano-device. However, for research and industrial application of the transition metal chalcogenides, a large scale growth technique is essential. Up to now, transition metal chalcogenides are being fabricated by using techniques like chemical vapor deposition, physical vapor deposition, or atomic layer deposition. However, it is difficult to fabricate a uniformly high-quality large-scale 2-dimensional semiconductor.
MoS2, which is one of the most popular transition metal dichalcogenides, is a material having a planar structure including three atomic layers one Mo atomic layer and two S atomic layers above and below the Mo atomic layer, where the three atomic layers constitute a hexagonal crystal structure. MoS2 is one of the most popular 2-dimensional semiconductor material that can exhibit bipolar characteristic due to the availability of both electrons and holes as carrier charges, and a thin film of MoS2 is mainly used as a p-type semiconductor. MoS2 is reported to have a theoretical mobility up to 400 cm2/Vs, has a high Ion/Ioff equal to or above 108, and is being an attractive semiconductor material applicable to a transparent and flexible device. Furthermore, a bilayer or higher-order MoS2 structure exhibits an indirect bandgap (about 1.3 eV), whereas a monolayer MoS2 structure exhibits a direct bandgap (about 1.9 eV) and excellent photoluminescence characteristic. In this view, MoS2 may also be applied to an optoelectronic device. Furthermore, MoS2 is expected to be utilized in various fields including the valleytronics. Examples of MoS2 synthesizing methods include top-down methods and bottom-up methods. Although the most popular top-down method is a mechanical exfoliation, but it is difficult to use the method for mass production. Meanwhile, bottom-up methods have problems including complicated operations and high costs.
Conventionally, solid powders of a transition metal, such as Mo or MoO2, and sulfur powders are together vaporized at a high temperature and are synthesized on a substrate. However, it is difficult to fabricate a uniform large film with such a common synthesizing method. In particular, it is difficult to uniformly deposit a transition metal by the method, and thus a film cannot be uniformly formed on a substrate. In the method, solid powders are disposed in a reactor and is vaporized toward and synthesized on a substrate. In this case, composition of the synthesized film varies according to locations of the substrate, and thus a uniform thin-film cannot be formed throughout the substrate. Furthermore, the thickness of the film formed by using such a method becomes so large (e.g., equal to or greater than about 10 nm), grains size of the film is so small (e.g., a few 10˜a few 100 nm) and the electrical property is so poor that the method cannot be efficiently utilized.